While bearings are the best, they are not necessary. I have some shop-made skates and the wheels are 3" stock with holes drilled in them. The axles are stock also, but have holes and grooves in them to allow the grease, squirted in from the ends where there are grease fittings, to spread out along the axles. Greasing the axles makes a huge difference. The frame around the wheels is 1/2" steel. These things are beasts and weigh around 50 lbs each. I also have a caterpillar style, like the Hilmans that works well too. No way to grease the axles in that though.
If you go with bolts and no bearings, make sure the wheels do no bear on the threaded area of the bolts. It will wear quicker.
Chris